The present invention relates to a printing apparatus comprising a DC power source device, which drives a printhead (recording head) of an inkjet printer.
An inkjet printing method is advantageous because it enables high-speed printing, makes almost no noise at the time of printing, enables direct printing on regular paper and does not require a fixing process so as to enable downsizing of a printer. Owing to these advantages, commercialization of the inkjet printing method is increasing. The inkjet printing method includes: a method which utilizes an electric/mechanical converter for jetting an ink droplet from a nozzle by making use of a motion caused by mechanical changes induced by input signals; and a so-called thermal inkjet method employing electrothermal transducers (heating resistances) for discharging an ink droplet by a pressure of bubbles generated on the heating resistances which generate heat upon application of a voltage pulse.
A known ink discharge method of an inkjet printer is to heat resistances or resistors by electric power applied to a printhead and discharge ink from a micro-nozzle by utilizing bubbles generated within the nozzle serving as an ink channel. In this case, to drive a printhead for discharging ink, a constant DC voltage is applied to the resistances to turn on/off switch devices connected in series to the resistances, thereby supplying the amount of power necessary for ink ejection to the heater resistances.
The printhead of an inkjet printer, which has a removable configuration, is held in a carriage unit moving in accordance with a width of a print medium, e.g., paper, at the time of printing. Therefore, a printhead set in a printer is not always the same. For instance, a printhead for printing black and white images, a printhead for printing color images, and so on, may be used for its purpose.
Since an arbitrary printhead is mounted as described above, the amount of head driving power necessary for discharging ink in a single discharge operation is controlled in order to stabilize the printing operation regardless of a variation in resistance values of the heater resistances in the printhead. Conventionally, the amount of electric power is controlled by detecting a variation of the heater resistance values based on a resistance value of a detection resistance, provided within the printhead that includes the heater resistances, then inputting the variation data to a control circuit provided on a main board fixed to a printer main body, and adjusting a head driving pulsewidth transmitted from the main board to the printhead.
Furthermore, an amount of heater driving power is also controlled by detecting a temperature rise in a printhead with the use of a thermometer, provided within the printhead that includes the heater resistances, and adjusting a head driving pulsewidth transmitted from the main board to the printhead.
Note that the DC voltage applied to the heater resistances is supplied as a constant voltage from an AC adapter or a DC power source device provided within a printer.
FIG. 7 is a block diagram showing a brief construction of an example of a conventional inkjet printer. In FIG. 7, reference numeral 51 denotes an inkjet printhead; 52, a head carriage circuit board; 53, a head carriage; 54, a flexible cable; 55, a main board of the printer main body; 56, a driving pulse control circuit included in the main board 55; 57, a power source; and 58, a host apparatus.
The inkjet printhead 51, having a plurality of heating resistances, performs printing by discharging an ink droplet from a nozzle by making use of a pressure of bubbles, generated by converting energy to heat, the energy being supplied from the power source 57 in accordance with controlling of the driving pulse control circuit 56 in the main board 55.
The main board 55 converts an image signal, transmitted from the external host apparatus 58, to a bit signal which turns on/off each of the heating resistances in accordance with, for instance, a print mode or the like, and transmits the bit signal to the driving pulse control circuit 56 for generating a driving pulse. The driving pulse consists of, e.g., a heat source selection signal, printing serial signal, and so forth. The pulsewidth of the driving pulse is changed in accordance with information, such as a temperature of the inkjet printhead 51, so as to perform most appropriate ink droplet discharge.
The generated driving pulse is transmitted to the head carriage 53 through a movable cable such as the flexible cable 54, and transmitted to the inkjet printhead 51 through the head carriage circuit board 52. The inkjet printhead 51 is constructed with one or more removable head units. The head carriage 53 is structured such that it is movable. The head carriage circuit board 52 mainly serves as a relay for electrically connecting the flexible cable 54 with the inkjet printhead 51.
The power source 57 adopts an AC/DC converter having plural outputs for supplying a power source voltage to logical circuits such as the main board 55, motors (not shown), and inkjet printhead 51. Voltage precision is required particularly for the voltage supplied to the inkjet printhead 51, in view of an influence of a voltage drop caused by wiring resistances generated as a result of passing through the long flexible cable 54 and also for stable ink droplet discharge.
FIG. 8 is an explanatory view of connection between heating resistances and driving switches in the example of the conventional inkjet printhead.
In FIG. 8, reference numeral 16 denotes a heating resistance; 17, a driving switch; and 18, a power source line connected to a power source. Reference numeral 19 denotes a heating resistance driving circuit connector. One end of the heating resistance 16 is connected to the power source line 18 which receives voltage supplies from the power source, and the other end is connected to the driving switch 17.
Assume herein that the inkjet printhead has 64 nozzles. One end of the heating resistance 16, corresponding to each of the 64 nozzles, is connected to the power source line 18 which supplies a driving voltage, while the other end of the heating resistance 16 is connected to the driving switch 17. The heating resistance driving circuit connector 19 is connected to a heating resistance driving circuit (not shown) for being controlled such that a current is sent only to the heating resistances 16 selected in accordance with the heat source selection signal or printing serial signal transmitted from the main board. Note in FIG. 8, nozzles are numbered (N#1 to N#64) from the left.
FIG. 8 shows an example in which the 64 nozzles are divided into 8 blocks each having 8 nozzles, and nozzles are driven in block unit. In FIG. 8, nozzles N#1 to N#8 are included in block 1, N#9 to N#16 are in block 2, . . . , and N#57 to N#64 are in block 8.
Depending on an image to be printed, 8 nozzles in each block may be driven simultaneously. Among the signals outputted from the driving pulse control circuit 56, the heat source selection signal is used for determining a block to be driven in the 8 blocks, and the printing serial signal is used for selecting a nozzle discharging ink from the 64 nozzles. The amount of current sent through the power source line differs in accordance with the number of nozzles driven simultaneously. Therefore, even in a case of driving one block, a voltage drop level caused by wiring resistances is different depending on the number of nozzles driven in the block. Also, a sudden variation in the amount of current affects the voltage drop level.
As mentioned above, a voltage drop level differs in accordance with the number of nozzles driven in each block. Conventionally, the voltage drop level is corrected by controlling a driving pulsewidth so as to supply uniform heating energy (power) to the heating resistances of the nozzles. This construction is disclosed in, e.g., Japanese Patent Application Laid-Open No. 9-11463.
According to a conventional printhead driving method, a DC voltage for driving a printhead is supplied to the printhead through a flexible board, which connects the main board with a movable carriage board. The flexible board has a long wiring structure because it requires at least a length corresponding to the stroke of printhead""s movement. Supplying a DC voltage for driving the printhead through such long wiring causes a problem of a voltage drop due to a wiring impedance. Because a head driving current is increasing in response to demands for high-speed and high-quality printers, an influence of the aforementioned voltage drop has come to the fore.
Furthermore, as means to control the amount of head driving power necessary for discharging ink in a single discharge operation, a method of adjusting a driving pulsewidth in accordance with a state of a printhead is adopted. However with this method, it is necessary to secure a maximum time width for a pulsewidth driving the heaters so as to make correction on the pulsewidth in accordance with various factors. This causes a problem of limiting the number of nozzles which can be used for printing per unit time, and as a result, limiting printing speed.
In addition, as mentioned above, a level of voltage drop caused in accordance with the number of nozzles driven in each block is corrected by controlling a driving pulsewidth so as to supply uniform energy to heating resistances of the nozzles. However, according to this method, it is controlled such that a driving pulsewidth is increased when a large number of nozzles is driven simultaneously. This makes a pulsewidth large (in other words, long time), holding from increasing the speed of an inkjet printer.
The present invention has been proposed in view of the conventional problems, and has as its object to provide a printing apparatus integrally comprising control means on a carriage unit, for continuously supplying a stable amount of power necessary to control printing operation without controlling a head driving pulsewidth, by variably controlling a driving voltage for driving a printhead.
Another object of the invention is to provide an inkjet printing apparatus, which comprises means for having an inkjet printhead detect a variation of a plurality of heat source elements and having a DC/DC converter detect the number of simultaneously-driven heat sources, and which performs controlling by making an output voltage of the DC/DC converter variable in accordance with detected information so as to control the amount of power supplied to heating resistances (heater resistances) to the most appropriate value for ink discharge.
In order to achieve the above objects, a printing apparatus according to the present invention has the following configuration.
More specifically, the present invention provides a printing apparatus which performs printing by scanning a carriage unit, having a printhead and a voltage control unit controlling the printhead, over a print medium based on information transmitted by an external apparatus, the voltage control unit comprising: reception means for receiving an information signal transmitted from the printhead; and voltage generation means for generating a driving voltage which is adjusted to drive the printhead based on the information signal received by the reception means.
According to an aspect of the present invention, the voltage generation means is a DC/DC converter which transforms a DC voltage to be applied to the printhead into a value appropriate for driving a mounted head.
According to another aspect of the present invention, the information signal includes an identification signal for identifying a type of the printhead, and the voltage generation means controls the driving voltage in accordance with the identification signal.
According to another aspect of the present invention, the information signal includes a signal indicative of a variation of a plurality of heater resistances provided in the printhead, and the voltage generation means controls the driving voltage in accordance with the signal.
According to another aspect of the present invention, the information signal includes a signal indicative of temperature data of the printhead, and the voltage generation means controls the driving voltage in accordance with the signal.
According to another aspect of the present invention, a detection resistance is provided inside the printhead for detecting a variation of the heater resistances, and the voltage generation means comprises an internal resistance connected in series with the detection resistance, wherein the voltage generation means compares a reference voltage, divided by the internal resistance and the detection resistance, with a driving voltage which drives the printhead, then controls the driving voltage so as to cancel an error in these voltages, and adjusts the driving voltage in accordance with a variation of a load resistance value of the printhead so as to correct the variation.
According to another aspect of the present invention, the printhead includes a diode for detecting a temperature, and the voltage generation means comprises an internal resistance connected in series with the diode, wherein the voltage generation means compares a reference voltage, divided by the internal resistance, detection resistance provided inside the printhead, and diode, with a driving voltage which drives the printhead, then corrects an error in these voltages, and generates a control voltage for optimizing power supplied to heat the printhead, so as to discharge ink in accordance with a temperature variation of the printhead.
According to another aspect of the present invention, the printing apparatus further comprises: a plurality of heat sources for generating bubble generation heat for driving in nozzle unit; driving pulse generation means for generating a pulse train which drives the plurality of heat sources; and heat source number detection means for detecting a number of plurality of heat sources driven simultaneously, wherein the voltage generation means adjusts a voltage outputted to the heat sources based on a signal from the heat source number detection means.
According to another aspect of the present invention, the heat source number detection means detects the number of plurality of heat sources driven simultaneously based on an image data signal.
Furthermore, according to the present invention, the foregoing object is achieved by providing a printing apparatus which performs printing by scanning a carriage unit, capable of holding a printhead having a plurality of nozzles discharging ink, over a print medium based on information transmitted from an external apparatus, a body of the carriage unit comprising: heat source detection means for detecting a number of heat sources driving the nozzles; and voltage generation means for supplying a voltage to a heat source for driving the nozzles, in accordance with the number of heat sources detected by the heat source detection means.
Still further, according to the present invention, the foregoing object is achieved by providing a printing apparatus forming an image on a print medium by supplying an electric energy necessary for printing to a heating resistance of a printhead, comprising: a switching device for controlling each heating resistance; a printhead including a detection resistance for detecting a variation of a resistance value of the heating resistances; a voltage variable circuit for adjusting a power source voltage, applied to the heating resistance, in accordance with the resistance value of the detection resistance so as to apply energy appropriate for printing; and a head driving power source circuit for comparing a first voltage value, generated by dividing a reference voltage by the detection resistance and a resistance provided outside the printhead, with a second voltage value, generated by dividing an output voltage of the head driving power source driving the printhead by a resistance, and controlling an output voltage so as to cancel a difference between the first voltage value and the second voltage value, wherein a GND-side end of the detection resistance provided inside the printhead is connected as a common wiring with a GND wiring transmitting a driving current of the printhead.
According to an aspect of the present invention, the GND-side end of the detection resistance connects with the common wiring transmitting a load current in an internal portion of the printhead, and the detection resistance does not have a dedicated outgoing contact pad on a GND-side terminal.
According to another aspect of the present invention, in a case where the GND-side end of the detection resistance connects with the common wiring transmitting a load current in an external portion of the printhead, the connection position is located in the middle of the printhead and an output voltage stable point of the power source circuit.
According to another aspect of the present invention, a ratio of a wiring resistance value of the common wiring to a wiring resistance value of all wirings, connecting the power source circuit with the printhead and transmitting a head load current, is appropriately set in accordance with an output voltage so as to cancel a voltage drop in a load due to a wiring resistance.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.